It is expected to continue to search for secondary fungal metabolites with cytochalasin or cytochalasin-like biological activity. Currently available cytochalasin D-producing strains of Zygosporium masonii will, by culture modification, be induced to biosynthesize CD analogs. Chemical modification of CD with a view towards preparing immobilized matrixes or site-alkylating reagents will be undertaken. The latter compounds will be used for affinity-chromatographic retardation of cytochalasin receptor macromolecules, and for labeling specific binding sites on presumptive protein or glycoprotein binding species. An intensive kinetic study and chain localization of CD interaction with myosins has already been initiated. A systematic examination of the phylogenetic spectrum of activity of CD, with especial emphasis on lower eukaryotes, will be undertaken. Further delineation of the functional and molecular biological receptors located in cell membrane fractions will be mounted. In the latter work, reliance will be placed upon the continued use of H3-CD, and a variety of physical-chemical fractionation techniques.